Heavy oil and bitumen account for more than double the resources of conventional oil in the world. Recovery of heavy oil and bitumen is a complex process requiring products and services built for specific conditions, because these fluids are extremely viscous at reservoir conditions (up to 1500000 cp). Heavy oil and bitumen viscosity decreases significantly with temperature increases and thermal recovery methods seems to be the most promising ones.
Steam Assisted Gravity Drainage (SAGD) offers a number of advantages in comparison with other thermal recovery methods. Typical implementation of this method requires at least one pair of parallel horizontal wells drilled near the bottom of the reservoir one above the other. The upper well, “injector”, is used for steam injection, the lower well, “producer”, is used for production of the oil. SAGD provides greater production rates, better reservoir recoveries, and reduced water treating costs and dramatic reductions in Steam to Oil Ratio (SOR).
One of the problems that significantly complicate the SAGD production stage is possibility of the steam breakthrough to the producer. To handle this problem production process requires complicated operational technique, based on downhole pressure and temperature (P/T) monitoring. P/T monitoring data itself do not provide information about production well inflow profile, possible steam breakthrough and location of steam breakthrough zone. P/T measurements interpretation requires full scale 3D SAGD simulation which can not provide real-time answer. Simplified SAGD models (see, for example, Reis L. C., 1992. A steam Assisted Gravity Drainage Model for Tar Sands: Linear Geometry, JCPT, Vol. 13, No. 10, p. 14.)] can be used as the alternative to the SAGD 3D simulations, but existing SAGD simplified models do not account for the transient heat transfer to the reservoir and overburden formation during SAGD production stage and do not account for the presences of the water in formation. Thus P/T interpretation based on these models provides overestimated oil production rate (does not show oil production rate decrease in time) and can not give estimation of the water production, so do not provide information about SOR.